1. Field of the Invention
The present invention relates to textile material useful for producing composite laminated articles by injection molding, and more particularly by vacuum injection. This invention also relates to a process for producing such composite laminated articles by injection molding as well as the articles obtained comprising such a textile material.
Generally, conversion technologies for producing laminated (or composite) articles, that is to say materials having a textile reinforced resin base, can be grouped in two main categories, namely:
(a) those making it possible to produce articles at high rates, mainly involving the use of polyester or thermoplastic type resins reinforced with short fibers and processes such as compression, injection, and stamping, among others;
(b) those making it possible to produce articles at low rates, involving the use of sheet, webs, fabric or matt type-textile materials, and processes such as molding in an autoclave, by contact, in a vacuum, and other known molding techniques.
Of the technologies of type (b), the so-called "contact" processes are often relatively limited with respect to reliability and reproducibility and moreover, cause much pollution.
It should also be noted that in the technologies of type (b) labor is a large component of the final cost of the article.
However, the technologies of type (b) produce, as a whole, articles having mechanical properties that are better than those exhibited by articles produced by means of the high-rate processes of type (a).
There is therefore a tradeoff between mechanical properties and production rates in producing such articles, and in the present state of the art it has not been possible to find any satisfactory compromise between these two requirements. As a result of trends in the market for composite articles, there is a demand for technologies and materials making it possible to produce articles having high quality characteristics at sufficiently high production rates.
For some years, particularly in the sports and leisure industries, it has been proposed to produce large series of molded articles by the so-called "injection" technique, in particular using glass mats as reinforcing textile materials and polyester resins. The advantage of such a technology is that only a moderate investment is required, high production rates are possible, it can easily be automated, it does not cause pollution and the results are easily reproducible with high reliability. Although this technique is satisfactory when articles having relatively low mechanical properties are to be produced, when articles having a very high strength, that is to say having a high content of reinforcing textile material, are to be produced, it has been found that it is difficult and even impossible to carry out such a technique, since the textile reinforcements form a barrier preventing the resin from circulating and therefore preventing a complete and homogeneous impregnation of the reinforcements.
A reference illustrating the state of the art in the field of vacuum molding with resin injection is U.S. Pat. No. 2,913,036 which discloses a process for producing large-size articles, such as tanks or swimming pools. To make it easier to introduce the resin into the mold, it is proposed to provide a network of perforated tubes ensuring that the liquid resin is distributed more uniformly within the article during molding. This patent therefore describes a molding technique of the type described above, which cannot be used for producing composite materials comprising a stack of textile reinforcements. The technical problems raised are completely different if production rates sufficient for the industrial production of textile material are to be achieved.
To solve these problems, various methods have already been proposed which involve either injecting the resin under high pressure or making it highly fluid to allow it to penetrate more easily, or which involve a combination of the two. It has also been proposed to modify the textile reinforcements, for example by processing the fibers or the reinforcements chemically, carrying out preimpregnation of the various reinforcing layers, keeping the elementary filaments of the threads of the reinforcing fabrics as flat as possible and as parallel to one another as possible, and even producing perforated materials.
Although the proposed solutions may yield satisfactory results in some cases, it is nevertheless appropriate to note that, in general, these results are achieved at the expense of one or more relevant parameters of the injection-molding technique (more complex reinforcements, low-performance resin, high investment, etc.).